The invention relates to a rock drill for hand-guided rotary hammers, percussion drilling machines or rotary drilling machines.
A known rock drill consists of a helical shank and a drill head in which a carbide cutting element, roof-shaped in side view and extending over the entire drill nominal diameter, is inserted (DE 197 34 094 A1). For this purpose, the drill head has an axially running, slot-shaped recess, into which the carbide cutting tip is inserted and brazed in place.
In order to achieve adequate endurance of the drilling tool, the carbide cutting tip must have a certain minimum thickness, a factor which necessitates a correspondingly wide locating slot for the carbide cutting tip. However, such a locating slot extending over the entire diameter for the carbide cutting tip reduces the wall thickness available at the drill head for supporting the carbide cutting tip.
Powerful rock drills require conveying helices having a high volume of the conveying helix flutes in order to permit the removal of as high a quantity of drillings as possible. A high flute volume is achieved by a large flute depth, which, however, leads automatically to a smaller core thickness of the remaining core cross section of the conveying helix.
If such a flute cross section were to be run with uniform flute depth right into the top region of the drill head, there would be no material at the drill head, on account of the uniform conveying helix web, in order to embed a carbide cutting tip if possible on both sides and completely in the drill head. For this reason, the conveying helix, for example according to the representation in FIGS. 4, 5 and 7 of said DE 197 34 094 A1, is not run right into the front region of the drilling tool or drill head but rather ends at a certain distance below the drill head and in particular below the slot root for locating the carbide cutting tip. In a representation according to the prior art, this is-shown schematically in FIGS. 2a, 2b of the present invention. When the drilling tool is being produced, the helix angle xcex1, measured toward the drill longitudinal axis, of the conveying helix in the region of the drill head is therefore run toward zero; that is to say that the profile grinding wheel used to produce the conveying helix flute and set at an angle is backed out virtually parallel to the axis of the drill head in the end region of the conveying helix without the drilling tool still rotating in this region. The conveying helix is therefore not continued up to the front end of the helical shank but is designed as a type of flat, chisel-shaped point. Owing to the fact that the conveying helix is not continued up to the front region of the drill head, the land of the conveying helix widens in this region, so that material for locating and embedding the carbide cutting tip is obtained. This is shown for the prior art in FIGS. 2a, 2b in each case in side view.
Such production therefore leads to a flat, chisel-shaped drill head in which a corresponding longitudinal slot for locating the carbide cutting tip can be made. In this case, the transition between carbide cutting tip and conveying helix can be ground, as shown with the surface sections 25, 26 in the above-mentioned FIGS. 4, 5, 7 of DE 197 34 094.
On account of this configuration of the drill head or of the transition between the conveying helix and the drill head, a type of chisel-shaped, that is to say flat, drill head geometry is produced, which has a high removing capacity. A disadvantage, however, is that the guidance properties of the drilling tool in this region are effected solely by the carbide cutting tip, since the region of the annular support of the conveying helix or of the helical shank is not present in this front flat region of the drill head, but only comes into effect when the fully formed conveying helix engages in the drill hole.
The object of the invention is to provide a drilling tool which does not have the above-mentioned disadvantages and in which, in particular just after the start of drilling, effective guidance of the drilling tool in the drill hole is also obtained in the drill head region. A further advantage is especially robust embedding of the carbide cutting tip.
This and other objects are achieved by a rock drill for hand-guided rotary hammers, percussion drilling machines or rotary drilling machines. The rock drill has a drill head having at least one locating slot, a carbide insert, and a supporting region of the carbide insert. The rock drill also has a single- or multi-start conveying helix having a flute and adjoining the drill head, and a clamping shank adjoining the conveying helix. The carbide insert extends at least in a direction transversely across the drill head and is embedded in the at least one locating slot. The drill head has a support for the carbide insert in a region of the embedding of the carbide insert. The conveying helix extends into the supporting region of the carbide insert, and a core thickness of the conveying helix flute increases toward the drill head.
The central idea of the invention is to continue the conveying helix as far as possible up to the drill point in order to thereby achieve optimum conveying and guidance properties of the drilling tool even in the drill head region. In this case, however, it must be ensured that adequate support, as far as possible over the full surface area, of a carbide insert embedded in the drill head is ensured, this carbide insert preferably being designed as a carbide cutting tip. These factors, which are actually inconsistent with one another, are harmonized by the land width of the conveying helix of the drill head being widened continuously or discontinuously, whichxe2x80x94with a preferably uniform helix angle of the conveying helixxe2x80x94is effected by a continuous increase in the core cross section or a corresponding decrease in the flute depth. This is done during the production of the drilling tool, e.g. by continuously backing the grinding or milling tool out of the conveying helix flute. In this way, the conveying helix web is widened toward the drill head, as a result of which the effective cross section for making a locating slot for the carbide cutting tip is increased.
Consequently, if the conveying helix in the prior art ends in the region of the slot depth for locating the carbide cutting tip, the conveying helix in the present invention is run well into the head region, that is to say beyond the level of the slot root. Nonetheless, the desired widening of the land surface occurs, so that an effective slot can still be made for the carbide cutting tip.
The conveying helix is consequently run right into the region of the surface sections for the lateral support of the carbide cutting tip. In this case, preferably no change in pitch relative to the helix angle of the conveying helix is carried out; that is to say that the helix angle is not brought to the value zero as in the prior art. The increase in the core strength of the conveying flute in the region of the drill head may be effected continuously or discontinuously. Normally this is carried out continuously by backing out the tool uniformly.
The increase in the core thickness of the conveying helix for forming adequate support for the carbide cutting tip is preferably effected in such a way that the carbide cutting tip is embedded on both sides, that is to say supported on both sides. Of course, the support is especially important in the region lying behind the flank of the cutting tip.
According to the invention, it is therefore necessary to have the conveying helix flute start directly in the region which is designed as a surface section for supporting the carbide cutting tip.
In a development of the invention, provision is made for the conveying helix to be of single- or multi-start design, encircling main webs and encircling secondary webs being formed which are preferably designed according to the earlier application of the applicant DE 197 53 731. Reference is expressly made thereto. In this prior art, the access to each secondary conveying flute and to the main conveying flutes is achieved by an extremely thin drill head, which is achieved by a straight, axially parallel runout of the conveying helix in the region of the drill head. The teaching according to the invention can also be advantageously realized in such a special conveying helix having the advantageous properties associated therewith. Further designs in this respect are specified in the subclaims. In this case, for example, the conveying edges of the main and/or secondary webs, to form bearing surfaces for drillings, preferably run approximately at right angles to the drill longitudinal axis. The secondary web of the secondary conveying helix may be designed with a land tapering to a point. However, other cross-sectional shapes may also be used for the secondary conveying helix, as specified in detail in DE 197 53 731.